Magnetic recording heads have utility in a magnetic disc drive storage system. Most magnetic recording heads used in such systems today are “longitudinal” magnetic recording heads. Longitudinal magnetic recording in its conventional form has been projected to suffer from superparamagnetic instabilities at densities above approximately 40 Gbit/in2. It is believed that reducing or changing the bit cell aspect ratio will extend this limit up to approximately 100 Gbit/in2. However, for recording densities above 100 Gbit/in2, different approaches will likely be necessary to overcome the limitations of longitudinal magnetic recording.
An alternative to longitudinal recording that overcomes at least some of the problems associated with the superparamagnetic effect is “perpendicular” magnetic recording. Perpendicular magnetic recording is believed to have the capability of extending recording densities well beyond the limits of longitudinal magnetic recording. Perpendicular magnetic recording heads for use with a perpendicular magnetic storage medium may include a pair of magnetically coupled poles, including a main write pole having a relatively small bottom surface area and a flux return pole having a larger bottom surface area. A coil having a plurality of turns is located adjacent to the main write pole for inducing a magnetic field between the pole and a soft underlayer of the storage media. The soft underlayer is located below the hard magnetic recording layer of the storage media and enhances the amplitude of the field produced by the main pole. This in turn allows the use of storage media with higher coercive force. Consequently, more stable bits can be stored in the media. In the recording process an electrical current in the coil energizes the main pole, which produces a magnetic field. The image of this field is produced in the soft underlayer to enhance the field strength produced in the magnetic media. The flux density that diverges from the tip into the soft underlayer returns through the return flux pole. The return pole is located sufficiently far apart from the main write pole such that the material of the return pole does not affect the magnetic flux of the main write pole, which is directed vertically into the hard layer and the soft underlayer of the storage media.
A magnetic recording system such as, for example, a perpendicular magnetic recording system may utilize a write pole with a square or rectangular cross-section. Under certain circumstances, the increased magnetic field concentration at the sharp corners can cause writing or erasure on adjacent tracks.
Another development that overcomes at least some of the problems associated with the superparamagnetic effect is heat assisted magnetic recording (HAMR), sometimes referred to as optical or thermal assisted recording. Heat assisted magnetic recording generally refers to the concept of locally heating a recording medium to reduce the coercivity of the recording medium so that the applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source. The heat assisted magnetic recording allows for the use of small grain media, which is desirable for recording at increased aerial densities, with a larger magnetic anisotropy at room temperature and assuring a sufficient thermal stability.
More specifically, super paramagnetic instabilities become an issue as the grain volume is reduced in order to control media noise for high aerial density recording. The superparamagnetic effect is most evident when the grain volume V is sufficiently small that the inequality KuV/kbT>40 can no longer be maintained. Ku is the magnetic crystalline anisotropy energy density of the material, kb is Boltzman's constant, and T is absolute temperature. When this inequality is not satisfied, thermal energy demagnetizes the individual grains and the stored data bits will not be stable. Therefore, as the grain size is decreased, in order to increase the aerial density, a threshold is reached for a given material Ku and temperature T such that stable data storage is no longer feasible.
The thermal stability can be improved by employing a recording medium formed of a material with a very high Ku. However, with the available materials, the recording heads are not able to provide a sufficient or high enough magnetic writing field to write on such a medium. Accordingly, it has been proposed to overcome the recording head field limitations by employing thermal energy to heat a local area on the recording medium before or at about the time of applying the magnetic write field to the medium. By heating the medium, the Ku or the coercivity is reduced such that the magnetic write field is sufficient to write to the medium. Once the medium cools to ambient temperature, the medium has a sufficiently high value of coercivity and assures thermal stability of the recorded information. When applying a heat or light source to the medium, it is desirable to confine the heat or light to the track where writing is taking place, and to generate the write field in close proximity to where the medium is heated to accomplish high aerial density recording. The separation between the heated spot and the write field spot should be minimal or as small as possible so that the writing may occur while the medium temperature is substantially above ambient temperature. This also provides for the efficient cooling of the medium once the writing is completed.
Accordingly, there is identified a need for an improved write pole with a shape and dimensions that overcome the limitations and shortcomings of known magnetic recording heads and heat assisted magnetic recording heads.